we were wading our way up the river and on the bank in front of us was this little animal eating a fish. It wasn't all that afraid of us and at one point jumped in the river and swam down our way before climbing out on the opposite bank.

We thought at first maybe it was a river otter but it looked too much like a weasel.

I'm thinking, after searching google, that it was a mink. I didn't know it but Utah has a wild population. I had never seen one before. Sounds like they have webbed feet and really do well in water.